66 



SCIENCE 



[N. S. Vol. XXIX. No. 732 



termined as male, female or hermaph- 

 rodite; while very many of the earlier ex- 

 perimental data have either failed of con- 

 firmation or have been shown to be suscep- 

 tible of a different interpretation from that 

 first assigned to them. Cjrtological and 

 experimental research combine to show, 

 not only that sex is predetermined in the 

 zygote, but also that it is in many cases 

 predestined (I do not here say predeter- 

 mined) in the gametes or even much 

 earlier. It is a familiar fact that in some 

 of the higher pteridophytes sex is pre- 

 destined in the microspores and megaspores 

 which produce, respectively, male and 

 female prothallia; and the same is, of 

 course, true of their homologues in the 

 flowering plants. It has likewise long been 

 known that in a few cases sex is similarly 

 predestined in eggs of two sizes in the 

 animals, for instance in Rydatina, Phyl- 

 loxera and Dinophilus apatris. But even 

 in cases where the germ-cells appear quite 

 alike to the eye it has been shown that a 

 sexual predestination may exist. A 

 primitive but perfectly definite predestina- 

 tion of this kind has, for instance, been 

 proved by Blakeslee to exist in both the 

 zygotes and the asexual spores of various 

 species of fungi ; and a similar predestina- 

 tion has been demonstrated also in some of 

 the more highly differentiated types, such 

 as the mosses and liverworts. As an 

 example of this I select the recent beautiful 

 studies of the Marchals on the dieeious 

 mosses. Isolation cultures prove that the 

 asexual spores, though similar in appear- 

 ance, are individually predestined as male- 

 producing and female-producing; and all 

 efforts to alter this predestination by 

 changes in the conditions of nutrition, such 

 as are known to be effective in the case of 

 fern prothallia, failed to produce the least 

 effect. Again, the remarkable experi- 

 mental results of Correns on dieeious 

 flowering plants ^Bryonia) prove that the 



pollen-grains, though apparently alike 

 morphologically, are predestined in equal 

 numbers as male-producing and female- 

 producing. Half the pollen-grains upon 

 fertilizing the eggs produce males and half 

 females. In the mosses the Marchals 

 demonstrate that all the products of a 

 single spore are likewise immutably de- 

 termined, since new plants formed by re- 

 generation from fragments of the pro- 

 tonema or from any part of the gameto- 

 phyte, are always of the same sex. Evi- 

 dently, sex is here a quality that pervades 

 all the cells of the organism, independently 

 of the external conditions. These results 

 tally with a considerable body of evidence 

 on the zoological side that all the products 

 of a single egg are of the same sex. This 

 is shown, for example, by the similar sex 

 of double monsters, and still more stri- 

 kingly by that of multiple embryos derived 

 from the same egg. The work of Bugnion, 

 Marchal and Sylvestri has shown that in 

 some of the ChaleidEe {Encyrtus, Lito- 

 mastix, Ageniaspis) each fertilized egg 

 produces large numbers of secondary 

 embryos by an asexual process. All of 

 those arising from a single egg are of the 

 same sex— female if the egg be fertilized, 

 male if it be unfertilized, as in the bee and 

 ant. 



m. CYTOLOGICAL BASIS OF THE SEXUAL PRE- 

 DESTINATION IN THE AIE-BREATHING 

 AETHROPODA 



In none of the cases just cited is any- 

 thing positively known of the cytologieal 

 basis of the sexual predestination in the 

 germ-cells. Our knowledge of this side of 

 the question is thus far confined to three 

 groups of the air-breathing arthropods, but 

 we here find a substantial basis for a 

 broader consideration of the entire prob- 

 lem. Cytologieal studies on insects, myria- 

 pods and arachnids have demonstrated that 

 in many of these forms a sexual predestina- 



